Glass is optically transparent, hardly transmits gas or moisture, and has excellent airtightness. Accordingly, glass is being used in the form of double insulating glass for window glass or display casing, or in packaging for covering a light-emitting element contained in electronic devices, for example.
When used for the above purposes, a plurality of glass members may be bonded with an internal space formed so as to increase thermal insulating property or airtightness. Because the bonding portions also require thermal insulating property or airtightness, a low melting point glass having excellent gas barrier property may be used as bonding material (sealing material).
For example, in Patent Literature 1, sealing material of low melting point glass is irradiated with laser so as to heat and melt the sealing material and to thereby bond glass members. Use of laser enables selective heating of only the laser irradiated portion, thus decreasing the thermal influence on portions other than the bonded portions. Because laser heating involves local heating, the temperature of the low melting point glass may be increased non-uniformly. As a result, thermal stress may be produced, whereby a failure of bonding with the glass members may readily be caused. Accordingly, a filler with low thermal expansion coefficient is added to the low melting point glass so as to avoid bonding failure.